Engine overheat opinion.

[kizerboy]

Looking for some opinions. End of last seson had a stud go thought the heat exchanger. Engine temp light came on as I slowed down to a normal speed, went into the snow to cool it off but the light did not go off until I shut it down. I got it all fixed up and ran the machine a week later. Everything ran good but buy that time it was time to store it for the summer.
Took it out of storage last week and decided to do a compression check on it and found that the psi was down to the minimum value 179 psi on three cyliders and 175psi on the 4th. put oil in the cyliders and they came up to 200psi. What would be the out come of this, just loosing some top end or engine detination? Do you think its will be ok to run it for the season if keep an eye on it? After all it is a Yamaha.

Thanks.

 

[mbarryracing]

I'd say it's more to do with leaking valves from the seats oxidizing from lack of running over the summer then any damage resulting in getting hot. If you weren't running it hard when it was overheating it didn't hurt it.

Run the engine for a while then do another compression test and you'll be amazed...

 

[mud99]

Kizer,
I'm not sure why, but I was never able to get a good consistent compression measurement on the Apex. My guage works fine on other vehicles, but the Apex is funny somehow - the readings would vary widely if I tested a few times.

If my understanding is correct it lowers compression for starting, maybe that is part of it.

I do like the idea of the oxidized valves, that might be the answer to the mystery. I tested after the sled had been stored for 4 months.

The sled runs great in general, so I don't think I have any sort of real problem.

Mark

 

[mbarryracing]

If you ever pull the exhaust manifolds off and look at the valves and ports after they have sat for a while, you'd initially consider pulling the head and doing a valve job they look so bad. But they clean themselves up after running for a bit, the oxidation burns off and they seat back in nicely.

I wouldn't be concerned, you'll take it out and find it will pull the right RPM's after a bit of running which indicates it's making the right power (clutches are mini dynos)

 

[kizerboy]

Thanks for the info guys. I'll see how it goes once we get some snow and take it for a good run.

 

[stevewithOCD]

Warm the engine to operating temp then re-test...